Run of pinch flats and I don't know why

[steverob]

Are you really sure you've not picked up another deflation-causer after those 30 miles?

First of all, these are not 'pinch flats'. You get these when your tyre is running too low a pressure - and you have yours at 100psi - or hit a pothole really hard, normally combination of the two.
This sounds like either your tyre or the rim tape is causing the puncture. When you remove the punctured tube, you must be able to find the puncture hole. That will show you where to look on the tyre/rim.
Must pre-inflate the inner gently before inserting.

I'll admit I'm making an assumption they are pinch flats based on what I know, which isn't exactly very much, but I'll explain what I do know and you can tell me if you think my assumptions are right or wrong.

Every time I have got a puncture before where it was caused by a thorn/glass/other debris, the way I've noticed has been the same - the repetitive "thud" noises while riding as the wheel turns, so then you get off the bike and notice the tyre already half deflated and eventually completely deflated anywhere between 10 secs and 10 minutes later depending on the size of the hole. Whereas the "bang fssssh" complete instant deflation is something I have only ever experienced twice before this current run of bad luck, and each time it was either on the same day as, or the ride after changing a tube from a "regular" puncture, which combined with the little round holes in the tube, has always led me to the assumption that these were caused by pinch flats.

As I may have said before elsewhere, I enjoy riding bikes, but I don't care much for fixing them (not just bikes, that goes for most things to be honest), so I've never really been all that bothered about learning more than doing the very basics, which is why I may have misdiagnosed this completely (or possibly diagnosed it correctly but it turns out it's completely my fault for not doing it right!).

When I get home (although given it'll be pitch black by then and there's not much light in our garage, I may have to wait until the weekend) I'll check to see if I still have the failed inner tubes and should be able to work out if the puncture marks were all in the same place. I know I still have one tube lying around, hopefully I didn't throw the others.

 

[mjr]

combined with the little round holes in the tube

I think most pinch flats I've seen have been pairs of slits rather than round holes, like this example:

"bang fssssh" complete instant deflation

That's been a blowout in my three experiences: slit tyre x2 and sharp valve hole edge; but I understand a pinched tube does a similar thing.

 

[Ajax Bay]

OP is pumping tyres up to 100psi, @User46386 . That is high enough unless they're 23s and he's 90+kg.
See Sheldon on types of puncture. I've described pinch flats (Sheldon calls them 'cuts') and @mrj has provided an image. Not to be confused with trapping a bit of the inner tube between the bead of the tyre and the rim 'hook'. If it's not repeated trapping (and mitigation for this is to give it five pumps and then check around the tyre/rim that it's seated correctly) from all you say on this and on the balance of probability, the cause of the flat is the same for each of these 3 consecutive occasions; something on the rim or (still) in the tyre is penetrating the tube. Sounds as if this doesn't happen till it's got the rider load on the wheel - often takes a bit of movement under load for the cause to penetrate. Some things causing a penetration act as a plug - the extent to which they do affects how quick/slow the deflation occurs - yours is 'quick'!
You need to see where the puncture is/was in your inner tube, relate that to the valve (ie in degrees) and then (even more) carefully check the inside (and outside) of the tyre (first) and then the rim/rim tape. They'll be two places to check as you didn't notice which way the tube was in the tyre. I'll assume you did not take the tyre right off or that you follow good practice of putting the main tyre make logo centred above the valve hole (for precisely this practical purpose).

Might be useful to know: make/model of tyre, weight of rider/bike combined, just to check 100psi is 'right'.

Sheldon (precised):
Keep track of which way the tube was facing in the tire, and pump it up. You will usually be able to find the hole by the hissing sound as the air escapes, or feel the blast of air on cheek, ear or lips. No? Immerse the inflated tube in water and look for bubbles (NB tube needs to be dry before any patching).
When you find the hole, make note of where it is with respect to the valve hole, also whether it is on the inner or outer side of the tube.

• If the hole is on the outer side of the tube, check the inside of the tire especially carefully in the area where the tube was punctured. It is very frustrating to install a new or patched tube and forget to remove the pointy object that caused the original problem!
• If you find two holes, one above another, you probably have what is commonly called a "snake bite," a pinch cut resulting from pinching the tube between the rim and a stone or pavement break. This sort of failure is most often caused by insufficient tire pressure.
• If the hole is on the inner side of the tube, check the inside of the rim. Although the rim tape is supposed to protect the tube from rim imperfections, sometimes it is not properly placed, and sometimes spoke ends can actually poke through the tape. Burrs and other sharp edges inside the rim can easily puncture tubes. If a rim has recessed spoke holes, the rim tape must withstand the air pressure in the tire.

 

[Tim Hall]

The "bang fshhhh", or more importantly the "bang" suggests to me that the tube is escaping from the confines of the tyre, expanding wildly and bursting. So check, as others have said, that your tyre is seated properly AND that the tube isn't trapped under the bead. I check for trapping by flexing the uninflated tyre away from the rim, towards the centre IYSWIM, and peering into the gap between tyre and rim wall. Not seeing the tube there is a Good Thing. Start at the valve and work your way round, then flip the wheel round and do the other side.

An alternative cause is a hole worn in the tyre case by a misaligned brake block. The tube can herniate out, get caught by a brake block and burst.

 

[Ajax Bay]

Agree your sentiment, Tim, but repeated trapping is a little unlikely and at least one would have produced more than 'two little holes' worth of damage to the tube. I'd like to think a hole in the sidewall would have been spotted during post flat tyre inspection (see OP).

 

[Tim Hall]

Agree your sentiment, Tim, but repeated trapping is a little unlikely and at least one would have produced more than 'two little holes' worth of damage to the tube. I'd like to think a hole in the sidewall would have been spotted during post flat tyre inspection (see OP).

Good point about repeated trapping. FWIW, several years ago I was perplexed for a several of weeks and multitude of punctures by a slit in the side wall caused by a badly aligned brake block. The hole in that case was a very narrow slit and hard to spot.

 

[steverob]

OP is pumping tyres up to 100psi, @User46386. That is high enough unless they're 23s and he's 90+kg.

Might be useful to know: make/model of tyre, weight of rider/bike combined, just to check 100psi is 'right'.

Bike plus rider and equipment all together should be pretty much on the 100kg mark right now (a few kilos lighter in summer!). Got Continental Gatorskins on the bike but they are 25mm's. Normally inflate them up to just a tad over 100psi, then add one more pump for good luck, assuming that I'll lose that much again as I fiddle with getting the pump off the valve.

 

[mjr]

assuming that I'll lose that much again as I fiddle with getting the pump off the valve

Unless you're using a pump head which depresses the valve tip while you're detaching it (rare on Presta), the tube pressure should close the valve as soon as the pump head pressure drops below it. If your pump head depresses the valve tip, change it once you can.

 

[Ajax Bay]

Bike plus rider and equipment all together should be pretty much on the 100kg mark . . . Continental Gatorskins on the bike but they are 25mm's. Normally inflate them up to just a tad over 100psi,

The BQ guide suggests 110psi rear and 90 front. You haven't said whether rear or front is getting these flats, but doubt these are pinch flats (because you'd know when you hit the pothole causing it/them). @Racing roadkill makes a good point: once "the tyre [is] back on, gently push the valve upwards and make sure it moves up and down freely, then just check the tyre is properly seated [bead in rims] at the valve point before you fully inflate the tube".

 

[Sbudge]

The "bang fshhhh", or more importantly the "bang" suggests to me that the tube is escaping from the confines of the tyre, expanding wildly and bursting. So check, as others have said, that your tyre is seated properly AND that the tube isn't trapped under the bead. I check for trapping by flexing the uninflated tyre away from the rim, towards the centre IYSWIM, and peering into the gap between tyre and rim wall. Not seeing the tube there is a Good Thing. Start at the valve and work your way round, then flip the wheel round and do the other side.

An alternative cause is a hole worn in the tyre case by a misaligned brake block. The tube can herniate out, get caught by a brake block and burst.

Good point, a hole in the tyre (whether caused by wear or damage) would be very hard to spot when deflated but would give the Bang/Pfft symtoms as soon as the herniated tube touched the road etc. and would repeat consistently with other tubes. I had that on a ride once. It was surprisingly hard to see until I realised what I was looking at, luckily I had a Park 'tyre boot' patch which did the trick nicely.

 

[Deleted member 1258]

One thing I haven't seen mentioned on this thread is the possibility that the OP has a split in the sidewall of the tyre, I think that it would be a good idea to check round once the tyre is inflated and make sure the tube isn't protruding though the tyre anywhere.

 

[Ajax Bay]

An alternative cause is a hole worn in the tyre case by a misaligned brake block. The tube can herniate out, get caught by a brake block and burst.

several years ago I was perplexed for a several of weeks and multitude of punctures by a slit in the side wall caused by a badly aligned brake block. The hole in that case was a very narrow slit and hard to spot.

One thing I haven't seen mentioned on this thread is the possibility that the OP has a split in the sidewall of the tyre

TMN award to @Tim Hall

 

[jonny jeez]

TMN award to @Tim Hall

I would add a split or hole in the tyre surface too. A small hole will become large enough under pressure for a tube to herniate through and cause a rapid deflation...bang, whoosh type of deflation that you describe. As the wheel rolls the herniated tyre (like a bubble) will pop if not on first, then on second contact with the road.

Edit...ahh I see I am three posts late with this suggestion.

 

[tyred]

I'd check the beading of the tyre very carefully. I've seen cases where the steel band is damaged and is poking through the rubber and puncturing the tube.

 

[Gravity Aided]

I would take a cotton boll and run along the inside of the tire, to see if there is something imbedded in the casing, perhaps microscopically small, that would cause the flat.